A well system can include a tubular string deployed in a wellbore and a flow modulation system at a surface location. The flow modulation system periodically varies a flow rate of fluid flowed in the wellbore. The flow modulation system comprises a motor and a variable flow restrictor driven by the motor. A method of advancing a tubular string in a subterranean well, the method comprising: pumping fluid through the tubular string and into a wellbore of the well; returning the fluid to a surface location; and flowing the fluid through a flow modulation system at the surface location, thereby producing fluctuations in a flow rate of the fluid.